We are investigating the molecular basis for the excitable response of most nerve and muscle cells. Our system is the frog heart. We are studying molecules responsible for the change of electrical properties of plasma membranes when they are stimulated. The most significant part of the response is an increase in sodium permeability (or the related conductance). The process of the transmembrane voltage dependent sodium conductance increase and decay can be affected at several points by quite specific inhibitors. We are utilizing these inhibitors to identify and analyze the molecular components of the amphibian myocardial plasmalemma which give rise to the conductance changes. An enriched plasma membrane preparation is used. This preparation is obtained by mild homogenization followed by low speed centrifugation, sucrose density gradient equilibrium centrifugation and washing. We will use modifications of the Weber Osborn SDS acrylamide gel system to separate and identify some 40 polypeptide constituents of various FCPM preparations using Coomassie Blue staining. We will use both cylindrical and slab gels. Earlier we have found of these some 15 bands are stained by PAS techniques and presumably at least these are glycoprotein. We have found that the polypeptides of this preparation are hard to dissolve and tend to aggregate. We will solubilize the proteins of the FCPM using 0.5 mM EDTA alone which we have found will solubilize around 50% of the plasma protein. We will separate and identify various solubilized proteins in detergent free gels. We are pusuing the separation of a STX binding site into the cytosol. This entity is probably a piece of the sodium channel, although this remains to be demonstrated.